现代移动通信网5

Forgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications无线移动通信的信道环境及其对系统设计的要求1.1无线移动的通信环境概述1.2路径损耗和阴影衰衰落1.3多径损耗1.4噪声和干扰Forgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications2Averagereceivepower----------coverageInstantaneousreceivedpower-------RTTForgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications3无线移动的通信环境概述Forgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications4多径衰落实测场强信号（数十波长范围内）1040短区间中值距离Forgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications5阴影衰落实测场强信号（数百波长范围内）1040短区间中心值变化距离Forgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications6传播损耗实测场强信号（数公里范围内）1040长区间中心值变化距离d(km)25101Forgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications7无线环境对信号的作用概述传输带来的问题：自由空间损耗阴影衰落多径衰落三种效应表现在不同的距离范围内外部干扰带来的问题：其他发射机的干扰：同道干扰，邻道干扰，互调干扰。环境噪声影响传输的地理环境：稠密市区市区郊区农村地理环境因素：地形形态植被密度建筑群密度空旷区水面Forgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications8传播模型大尺度模型（largescalemodel)一种简单理论和经验模型：对数衰落模型建立模型的基本方法：统计方法（平地传输模型，OkumuraHata模型；Cost231模型），直接计算和预测（射线跟踪法）。小尺度模型（smallscalemodel)平坦衰落的Clarke模型Forgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications9传播模型大尺度模型（largescalemodel)刻画在较大距离上的传播特征一种简单理论和经验模型：对数衰落模型建立模型的基本方法：统计方法（平地传输模型，OkumuraHata模型；Cost231模型），直接计算和预测（射线跟踪法）。小尺度模型（smallscalemodel)刻画在较小距离范围内的传播特征（几个波长）平坦衰落的Clarke模型Forgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications10路径损耗自由空间损耗——主要依赖于距离，频率因素理想的自由空间球面波扩散损耗2224lg10)(dGGdBPLrtForgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications11对数衰落模型00n0n0dd10nlog)(dLP(dB)LPdd(d)LP8n2,ddKPPtrForgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications12Forgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications13Okumura模型为预测城区信号时使用最广泛的模型。应用频率在150MHz到1920MHz之间（可扩展到3000MHz），距离为1km到100km之间，天线高度在30m到1000m之间。Okumura开发了一套在准平滑城区，基站有效天线高度为200m，移动天线高度为3m的自由空间中值损耗（）曲线。基站和移动台均使用垂直全方向天线，从测量结果得到这些曲线，并画成频率从100MHz到1920MHz的曲线和距离从1km到100km的曲线。使用Okumura模型确定路径损耗，首先确定自由空间路径损耗，然后从曲线中读出值，并加入代表地物类型的修正因子。模型可表示为：50()(,)()()FmutereAREALdBLAfdGhGhGmuA基站天线高度增益因子移动天线高度增益因子环境类型的增益传播路径损耗值的50％（即中值）自由空间传播损耗Forgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications14Okumura模型完全基于测试数据，不提供任何分析解释。它为成熟的蜂窝和陆地移动无线系统路径损耗预测提供最简单和最精确的解决方案。由于其实用性，在日本已成为现代陆地移动无线系统规划的标准。该种模型的主要缺点是对城区和郊区快速变化的反应较慢。预测和测试的路径损耗偏差为10dB到14dBForgraduatestudent,autumn,2010PCN&CADCenter,BeijingUniversityofPosts&Telecommunications15路径衰落对系统设计的影响正面：频率复用。使得资源可以在空间上复用。（早期的蜂窝技术和现在的频谱感知技术）解决了频谱资源受限的问题。频谱感知系统—认知无线电参考：DanijelaCabric，BerkeleyWirelessResearchCenter,UCBerkeley，“ResearchOpportunitiesinCognitive*Radios”EricHumphrey，“SpectrumEfficiencyandCognitiveRadio”一个新的概念：机会频谱系统不要混淆的一个概念：机会无线电系统WindowofOpportunityTime(min)Frequency(Hz)ExistingspectrumpolicyforcesspectrumtobehavelikeafragmenteddiskBandwidthisexpensiveandgoodfrequenciesaretakenUnlicensedbands–biggestinnovationsinspectrumefficiencyRecentmeasurementsbytheFCCintheUSshow70%oftheallocatedspectrumisnotutilizedTimescaleofthespectrumoccupancyvariesfrommsecstohoursSpectrumSharingExistingtechniquesforspectrumsharing:–Unlicensedbands(WiFi802.11a/b/g)–Underlaylicensedbands(UWB)–Recycling(exploittheSINRmarginoflegacysystems)Drawbacksofexistingtechniques:–Noknowledgeorsenseofspectrumavailability–Limitedadaptabilitytospectralenvironment–Fixedparameters:BW,Fc,packetlengths,synchronization,coding,protocols,…Newradiodesignphilosophy:allparametersareadaptive–CognitiveRadioTechnologyWhatisaCognitiveRadio（认知无线电）?Acognitiveradioisaradiothatcanchangeitstransmitterparametersbasedoninteractionswiththeenvironmentinwhichitoperates.ThemajorityofcognitiveradioswillprobablybeSDRs(softwaredefinedradios),butneitherhavingsoftwarenorbeingfieldprogrammablearerequirementsofacognitiveradio.–FCC.ETdocketno.02-25.Order,May2002Cognitiveradiorequirements–共存co-existswithlegacywirelesssystems–利用usestheirspectrumresources–不干扰doesnotinterferewiththemCognitiveradioproperties–检测RFtechnologythatlistenstohugeswathsofspectrum–感知Knowledgeofprimaryusers’spectrumusageasafunctionoflocationandtime–共享Rulesofsharingtheavailableresources(time,frequency,space)–服务质量保证Embeddedintelligencetodetermineoptimaltransmission(bandwidth,latency,QoS)basedonprimaryusers’behaviorFCCAnnouncementReleasedonDec30th2003,(ETDocketNo.03-108)FacilitatingOpportunitiesforFlexible,Efficient,andReliableSpectrumUseEmployingCognitiveRadioTechnologies“Werecognizetheimportanceofnewcognitiveradiotechnologies,whicharelikelytobecomemoreprevalentoverthenextfewyearsandwhichholdtremendouspromiseinhelpingtofacilitatemoreeffectiveandefficientaccesstospectrum”“Weseektoensurethatourrulesandpoliciesdonotinadvertentlyhinderdevelopmentanddeploymentofsuchtechnologies,butinsteadenableafullreali